1. Field of the Invention
This invention relates to apparatus for cutting indicia from tape and more specifically to a spring-tensioned support plate assembly for a dual roller arrangement for such an apparatus.
2. Description of Related Art
A prior apparatus includes a pair of pressure rollers, the diameter of one of which is slightly different than that of the other, mounted to a metal frame. One roller has a flat in the circumferential surface. The two rollers are geared with respect to each other in a 1:1 ratio. The pressure rollers are made from stainless steel to provide a proper frictional surface for the tape. The use of stainless steel allows some slipping relative to the pressure roller of tape inserted between the rollers while the tape is being pulled between the rollers. The tape is described more fully below. A certain amount of slippage of the tape relative to the roller is desirable so that the tape does not slip relative to the die plate, which causes wrinkling. Preferably the tape slips relative to the pressure roller the same as the die plate slips relative to its adjacent pressure roller.
The frame includes two pairs of upright metal posts, the posts in each pair being side by side and each pair being spaced apart from the other for supporting respective ends of the two rollers. A tightening bolt connects adjacent posts in each pair for tightening down the upright posts a sufficient amount depending on the die plate and tape thicknesses. The adjustment bolt serves to space the rollers sufficiently close and prevent significant separation of the rollers so that pressure developed by the rollers is sufficient to transfer the form of the letter from the die plate to the tape. The spacing is determined by the thickness of the tape, the thickness of the die plate, described below, used to form a character in the tape and the pressure required to be developed in the tape to produce the desired cutting action. The spacing also depends on the extent of spreading of the rollers as the tape and die plate pass in between.
A ratchet drive, including a crank, couples a handle on the crank to the pressure rollers to rotate the pressure rollers when the handle is turned. Assuming die guides support the die plate from below the rollers, the pressure rollers and the crank are geared so that turning of the crank in the forward direction pulls the die plate and tape upward between the rollers for forming an image. A further predecessor machine is described and claimed in U.S. Pat. No. 3,673,953, incorporated herein by reference.
A die plate having cutting lines for forming a character is placed between the rollers and supported and guided by die plate guides formed in the apparatus. A die plate is disclosed and claimed in U.S. Pat. No. 3,490,362, incorporated herein by reference. The die plate transfers pressure created by the pressure rollers through the cutting lines to the lettering tape. The character may be any discrete image such as a letter, number or design but will be assumed for purposes of discussion here to be a letter. The die plate includes drive lugs in the form of ridges formed in the die plate on each side of the letter. The drive lugs effectively increase the thickness of the die plate so that the pressure rollers more firmly grip the die plate. The drive lugs also preload the pressure rollers before cutting of the tape begins. The preloading develops the compressive pressure in the rollers prior to the point where the cutting lines come between the rollers. The die plate also includes a tape in the form of a uniform thickness label extending a given distance above the letter and a given distance below the letter. The label supplies a last increment of thickness of about three thousandths of an inch to the die plate on either side of the letter on the die plate without which the pressure rollers could not develop sufficient pressure to grip the die plate and tape before or after the letter is formed. If the die plate is placed between the rollers such that the label is below the rollers, the tape and die plate will not be pressed and rolled upward between the rollers. If the pressure rollers contact the die plate below the label, the tape and die plate will be advanced no further.
The die plate defines the interletter spacing for adjacent letters. The image spacing is defined by the distance between the leading edge of a given letter and the trailing edge of the letter and is unique for each type of letter. Every letter preferably has a constant post spacing defined by the length of that portion of the label following the trailing edge of the letter. This is the distance after each letter that the pressure rollers continue to pull the die plate and lettering tape upward. That portion of the die plate and the corresponding tape thickness are not sufficient to allow the rollers to continue pulling the tape and die plate upward. As soon as the end of the label is reached, the full gripping action of the pressure rollers is eliminated. Every letter is separated from adjacent letters a minimum distance equal to the post spacing. Each die plate includes a portion of the label in front of the leading edge of the letter. This amount is used to define a prespace according to the exact point on the label the pressure rollers pick up the die plate. If the rollers pick up the die plate closer to the leading edge of the letter, the prespacing will be less than if the rollers pick up the die plate further away. The combination of the post spacing of one letter and the prespacing of the next letter defines the interletter spacing.
The tape can be a three-layer tape such as that described in U.S. Pat. No. 3,558,425, incorporated herein by reference. The tape is suitable for forming any suitable character but will hereafter be called lettering tape. The tape is a three layer bi-axially oriented tape wherein the letter is formed by the cutting lines on a die plate transferring the pressure of the pressure rollers through the top layer without breaching the first layer either fracturing or bursting the second layer and leaving the third layer intact. The tape is mounted to a spool having friction discs such as a slip clutch mechanism for controlling the play out of the tape in response to the pulling force by the pressure rollers on the end of the tape. The tape and spool are mounted in a bracket in the apparatus. The lettering tape is inserted between the pressure rollers to form, along with the die plate, a letter in the tape as the die plate and tape are pressed and rolled between the rollers. The pressure rollers create pressure on the die plates and tape to transfer the letter from the die plate to the tape.
As the rollers rotate, the tape is advanced through the rollers a given distance. That distance is defined by the spacing of the letter and its pre- and post spacing. The interletter spacing between the letter and the immediately preceding letter is determined by the post spacing of the previous letter and the prespacing of the letter in question. The interletter spacing between the letter and the next succeeding letter is define by the post spacing of the letter and the prespacing of the next succeeding letter, what ever it may turn out to be.
A knob is provided for adjusting the prespacing for the next letter to be formed. This then defines the interletter spacing between the preceding letter and the one about to be formed. The knob increases beyond a given level the starting point at which the die plate is first fully contacted and therefore the amount by which the die plate is pulled between the rollers. The image spacing and the post spacing is a constant for a given letter. As noted at column 5, lines 25 et seq. of the '953 patent, no additional feed mechanism is required over the pressure rollers, tape, and the die plate.